Novel gold alloys and potentiometer wires produced from them



NOVEL GOLD ALLOYS AND POTENTIOMETER WIRES PRGDUCED FROM THEM No Drawing. Application February 4, 1958 Serial No. 713,099

7 Claims. (Cl. 75165) The present application is a continuation in-part of my copending application, Serial No. 607,976, filed September 5, 1956, now abandoned, which is in turn a continuation-in-part of my prior application, Serial No. 524,- 279, filed July 25, 1955, now abandoned, which is in turn a continuation-in-part of my application, Serial No. 441,- 627, filed July 6, 1954, now abandoned.

The present invention relates to novel gold alloys and to novel and improved potentiometer resistance elements and wires prepared from these alloys. These potentiometer resistance elements or wires are ideally suited for the construction of otentiometers, including those delicate potentiometers employed in telemetering devices, electronic computers and the like, as in electromechanical transducers employed to translate motion into changes of electrical characteristics.

In the construction of delicate and precise potentiometers and variable resistors it is very important if desirable results are to be obtained that the resistance element or wire employed have a low or controllable temperature coeflicient of resistance, i. e., the variation in resistance ice alloys of gold, and potentiometer resistance elements and wire prepared from said alloys, which will have substantially all of the hereinabove mentioned desirable properties.

It is another object of the invention to provide novel potentiometer resistance elements or wires which have optimum electrical, physical and chemical properties, including low temperature coefi'icients of resistance.

Other objects and advantages of this invention will be apparent to those skilled in the art from the description which follows. c

In accordance with my invention I have discovered that alloys, composed primarily of gold (desirably between about 50% and 89.5%), with between about-6% and 12% of chromium along with a metal of the first triad of group VIII of the periodic chart totaling at least about 75% of the chromium concentration and from 6% up to about of the alloy, provide potentiometer wires and resistance elements which have a low temperature coefficient of resistance, high electrical resistance and work- Chromium 6% to 12% should be small when the element or wire is subjected to temperature changes. The temperature. coefficient of resistance is preferably as close to 0 p. p. m. as possible and desirably less than :30 p. p. m. as measured over the fundamental temperature interval of 0 to 100 C. The resistance element should have as high a resistivity as possible for many applications. It is also important that the resistance element or wire be easily workable and have a high tensile strength so that .it can be'drawn into an extremely fine wire and can be readily wound to form a variable resistance unit without danger of breaking. In addition, the resistance element or wire should be hard and it should not be subject to excessive Wear when used in conjunction with a sliding metal contact brush, so as to provide a long operational life. It should also have electrical stability so that electrical characteristics will not drift with the passage of time nor with exposure to abnormal temperatures, and the alloy should resist oxidation and atmospheric corrosion.

Another important prerequisite of such resistance elements or wires is freedom from noise when used in a sensitive potentiometer or the like. Noise results in part from sharp random voltage or resistance peaks which are generated as the slider contact surface traverses the resistance windings of the potentiometer. The noise is much more pronounced with wires made of certain metals and alloys than with others. The preferred alloysv of the present invention provide relative freedom from noise.

Many attempts have been made to produce potentiometer resistance elements and wires, and alloys from which to make them, which have all of the hereinabove mentioned properties. I have succeeded in producingalloys of gold which will impart these properties to a potentiometer resistance element or wire made from such alloys.

It is an object of the present invention to provide novel j chloride is a satisfactory flux.

Metals of the first triad of group VIII of the periodic chart 22% to 30%, more prefer An alloy in accordance with the present invention containing 10% chromium, 25% nickel and 65% gold is the most satisfactory alloy produced to date. Potentiometer wires produced from it have no measurable noise and have excellent life, are easily drawn and not brittle, and have a low temperature coefficient of resistance,

The metals of the first triad of group VIII of the periodic chart are a well-known class which includes nickel, iron and cobalt. These metals have anatomic number of from 26 to 28 and are known as the transitional elements. The concentration of the metals of this class in the alloys of the invention may consist of a single metal or two or three metals of the group. Nickel is the preferred metal of the group.

I prefer to incorporate into the alloys of my invention small amounts of an element more electronegative than nickel and chromium, to act as a deoxidizer or degasifier. Such other element or elements include, but are not limited to, carbon, manganese, aluminum, zirconium, thorium, titanium and beryllium. Manganeseand aluminum are preferred. The desirable concentration of these elements is from about 0.001% to 1% of the alloy, although 0.2% is suflicient.

The alloys of the present invention may be prepared in accordance with the following process.

A high frequency induction furnace is satisfactory for the melting of the alloy. The melting of the components of the alloy may take place in a zirconium silicate crucible. The gold is melted first. A neutral flux is then added in sufiicient quantity to cover the molten gold. Dry barium One or more metals of the first triad of group VIII of the periodic chart and the chromium are then added until a uniform melt is obtained. The deoxidizer or other element is then added in slightly greater amounts than desired for the finished alloy to compensate for oxidation losses. during melting rolled to about half its original diameter.

Following the cold rolling of the ingot, I anneal it in an inert or reducing atmosphere, such as nitrogen or hydrogen gas, for about 15 minutes at 1,200 F. Rolling is repeated and until the ingot is reduced to a diameter of about 0.06 inches, with annealing treatments as necessary to impart ductility. The alloy; is then reduced into wire of thedesired diameter by drawing it throughdiamond dies in accordancev with the usual wire-drawing techniques. Where necessary during the drawing process, the wire is heat treated to relieve any stresses. When reducedfto the required diameter, the wire is again heat treated, enameled if necessary, andis then suitable for use in manufacturing rheostats and otentiometers, etc. No intricate baking step is required to, stabilize the temperature coefiicient of resistance of the wire or wound coil. The required stable electrical characteristics are produced in the present invention by means of varying the initial composition of the alloy.

. In order more clearly to disclose the nature of the present invention, specificexamples illustrating the present invention will hereinafter be described. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims. In each example theallo-ys, and the potentiometer wires produced from the alloys, are obtained in accordance with the hereinabove described process. In'each of the examples,.the temperature coefiicient of resistance was .measured over the fundamental temperature range. be-

tween and 100 C. andwas foundto be about :30 p. p. m. or less in eachcase.

Example 1 The alloy was produced by melting sufiicient .quantities of metals to produce'the following composition:

Percent Gold 65 Chromium Nickel, 25

Example 2 The alloy was produced by melting sufficient quantities of metals to produce the following composition:

Percent Gold 70 Chromium 10 Nickel 20 Sufiicient manganese was added to constitute an additional 0.2% of the alloy and the alloy drawn into a fine potentiometer Wire. This alloy has a resistivity of 615 ohms/ c. m. f.

Example 3 The alloy was produced by melting suflicient quantities of metals to produce the following composition:

7 Percent Gold 70 Chromium 6 Nickel 24 Sutficient manganese was added to constitute an additional 4 0.2% of the alloy and the alloy drawn into a fine potentiometer wire. The alloy has a resistivity of 450 ohms/ 0. 1n. f. I

Example 4 The alloywas produced by melting sufficient quantities of metals to produce the following composition:

Percent Gold 58 Chromium 12 Nickel 30 Sufiicient manganese was added to constitute an additional 0.2% of the alloy and the alloy drawn into a fine potentiometer wire. The alloy has a resistivity of 620 ohms/c. m. f.

Example '5 The alloy was produced by melting sufficient quantities of metals to produce the following composition:

Percent Gold 89 Chromium 6 Nickel 15 Sufiicient manganese was added to constitute an additional 0.2% of the alloy and the alloy drawn into a fine potentiometer wire. The alloy has a resistivity of 490 ohms/c. m. f.

Potentiometer wires or elements according to the present invention may be employed in rheostats, potentiometers and variable resistors of many. types, including the low torque toroidal resistor described in my U .8. Letters Patent No. 2,537,733, granted January .9, 1951.

The term potentiometer wire, as used throughout this application, is intended to include wire and other suitable forms of potentiometer resistance elements. The wires may take the form of various shapes, including fiat strips and the more conventional filaments of round Cross section.

Percentages of materials are expressed in percent by weight.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents ofthe' features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

What is claimed is: i

1. A gold alloy comprising between about 6% and 12% chromium, nickel in an amount of between about 22% and 30%, the remainder of the alloy being substantially gold which constitutes between about 50% and 72% of the alloy.

terms of 2. A gold alloy comprising between about 6% and.

12% chromium, nickel in an amount of between about 24% and 30%, the remainder of the alloy being substantially gold which constitutes between about'60% to of the alloy.

ganese, aluminum, zirconium, thorium, titanium and. beryllium.

5. A potentiometer having as a component a wire winding comprising a gold alloy in which gold constitutes the major proportion of the alloy, and which also contains between about 6% and 12% chromium and nickel in an amount of at least 75% of the chromium content and from about 6% up to about 30% of the alloy.

6. A potentiometer having as a component a wire winding comprising a gold alloy comprising between about 6% and 12% chromium, nickel in an amount of at least about 75% of the chromium concentration and from about 6% to about 30%, the remainder of the alloy being substantially gold which constitutes between about 60% to 80% of the alloy.

7. A potentiometer having as a component a wire winding comprising an alloy consisting essentially of about 20% nickel, 10% chromium and 70% gold.

References Cited in the file of this patent UNITED STATES PATENTS Hansen Nov. 24, 1925 Thomas June 2, 1936 FOREIGN PATENTS Great Britain "July 14, 1926 

5. A POTENTIOMETER HAVING AS A COMPONENT A WIRE WINDING COMPRISING A GOLD ALLOY IN WHICH GOLD CONSTITUTES THE MAJOR PROPORTION OF THE ALLOY, AND WHICH ALSO CONTAINS BETWEEN ABOUT 6% AND 12% CHROMIUM AND NICKEL IN AN AMOUNT OF AT LEAST 75% OF THE CHROMIUM CONTENT AND FROM ABOUT 6% UP TO ABOUT 30% OF THE ALLOY. 